The advent of multi-floored structures created a demand for stairway structures, and stairway systems are typically found in commercial, office, home and industrial environments. Due to the variety of sizes of stairway systems needed in today's environment, certain difficulties have been encountered in the design and fabrication of stairway systems; for example, riser sections in such stairways have to be exactly the correct height to fit each particular floor to floor height of the installation and still comply with regulatory laws. To simplify the process of constructing stairs individual step units or step modules capable of being joined together to form a pre-fabricated stairways have been developed. Examples of stair step modules which can be used to make a pre-fabricated stairway are described in the following list of patents:
______________________________________ U.S. Pat. No. Inventor Date of Issue ______________________________________ 1,304,33 Bois May 27, 1919 1,343,739 J. T. Nesdall June 15, 1920 2,206,862 Boyd July 9, 1940 3,381,775 Livers May 7, 1968 ______________________________________
While the above-referenced patents are suitable to make a pre-fabricated stairway, each of the individual step modules described in these patents have to be designed specifically for the installation in question, that is, the riser height of these various step modules is not adjustable. In commercial buildings and other structures, however, the floor to floor height varies anywhere between eight feet to fifteen feet with the variation in intervals as small as 1/4 inch. Historically, stairways had to be designed with the correct riser heights and individually produced to fit the floor to floor height specification of each installation. This method of producing stairways was time consuming and costly. It may be appreciated that it is therefore desirable to fabricate a stair step module which is a standardized component that can be fastened together with similar modules in such manner that the vertical height of the riser of each step module can be varied to suit the particular installation.
There has, in the past, been some development of step modules having adjustable riser heights for stair step assemblies. One such stair step module which is adjustable in riser height is shown in U.S. Pat. No. 3,608,256 issued Dec. 1, 1967 to Jefferys. In the Jeffery's patent a step module is shown wherein a step module is comprised of three separate parts. Each stair step module includes an inverted L-shaped portion having a downwardly depending leg with a plurality of spaced apart grooves extending rearwardly therefrom; and a reverse L-shaped riser having a horizontal leg and a vertical upwardly projecting leg having a plurality of spaced apart grooves extending forwardly therefrom; and a tread portion. The tread portion is adapted to interlock with the horizontal leg of the reverse L-shaped riser. The spaced apart grooves of the reverse L-shaped riser and the spaced apart grooves of the inverted L-shaped portion are adapted to be mated. When mated with one another the reverse and inverted L-shaped portions form a riser which can be adjusted to varying heights. Spaced apart grooves of the lower reversed L-shaped vertical leg are visible when the stair step assembly is formed into a staircase unless the riser height is the minimum riser height to which the stairway can be adjusted.
Another example of a stair step module is shown in U.S. Pat. No. 3,370,387 issued Feb. 28, 1968 to Sivley. Here, an adjustable riser height is shown wherein a two piece system is utilized to vary the riser height. One piece of the stair step module is a tread member with a rear edge riser portion that generally extends upwardly and terminates in an inverted "J" hook design. Another piece is formed as a riser member that depends from a second tread member in a vertically downward direction and that has a "J" hook flange. The inverted "J" hook riser portion extending from the lower tread and the flange on an adjacent riser mate with one another thus allowing simple installation and connection of the various stair step modules. The riser height with this inverted "J" hook mating system can be adjusted by welding the upper portion of the inverted "J" hook to the back portion of the riser. When the riser height is less than the maximum riser height allowed by the "J" hook mating system the inverted "J" hook does not rest securely inside the riser's "J" hook flange; therefore, the pressure and weight placed on the tread of the stair step assembly is held only by the weld on the back portion of the riser. The adjustment of the riser is further supported by the attachment of the stair step assembly to the lateral support or stringers; however, the force of the pressure on each individual step module is squarely felt on the weld between the mated portions of the two risers.
Despite the innovations shown in the various patents described above, there still remains a need for an improved standardized stair step module capable of being utilized in any on installations having different floor to floor height. There is also a need for a step module adapted to form an acoustically dampened, pre-fabricated stairway which is simple in construction, economical to manufacture and capable of withstanding industrial weight stair step traffic. Further, there is a need for a stairstep module in which the adjustable portion of the riser is completely out of view after installation, thus improving the appearance of the completed stairway and providing a strong and secure attachment of the stair step units.